In a treatment machine for terry or pile-type fabrics it is frequently necessary to accurately determine just where the pile or looped part of the textile ends and the pile-free edge region of the textile begins. This must be done when selvedging or trimming the goods and while the goods are invariably passing at a relatively high speed through the treatment machine.
German utility model 8,907,659 filed 22 Jun. 1989 and assigned to Carl Schmale GmbH (U.S. Pat. No. 07/777,563 filed 03 Dec. 1991) describes such an arrangement that is associated with a standard deflecting roll or beam of such a machine. The apparatus has one or more light sources that direct beams tangentially of the deflecting beam to respective photocells. The beams run just above the surface of the deflecting roll so that they are interrupted by the pile but not by the pile-less portion of the goods, making it possible to very accurately determine the location of the pile edge.
The deflecting roll can be fairly long so that it can be bent slightly out of position in some applications. In this case it is pulled away from the stationarily mounted light source so that same can give false readings, as it becomes possible for the pile part of the goods to slip between the beam and the roll.